1. Field of the Invention
The present disclosure relates to camera shake correction techniques suitable for use in image capturing apparatuses such as digital still cameras.
2. Description of the Related Art
As a method for correcting camera shake when exposure is performed for a long time, e.g., when image capture is performed in a dark place, for a digital still camera, a method that uses an image signal processing technique has been known.
For example, Japanese Unexamined Patent Application Publication No. 11-252445 discloses that a plurality of images are acquired in a time-division manner within an exposure time at the time of image capture, a motion vector for a temporally previous image is detected for each of the images, and each image position is superimposed and added based on the detected motion vector so that each inter-image positional deviation is cancelled.
With the above-described method, an image in which motion blur induced by camera shake at the time of image capture is reduced can be obtained. Hereinafter, the above-described camera shake correction method will be referred to as a “method of superimposing and combining continuously captured images”.
However, in the method of superimposing and combining continuously captured images, an exposure time for each of continuously captured images is reduced, and the proportion of noise included in an image capture signal read from an image capturing device is increased when the amount of light for an object is insufficient. Therefore, although motion blur can be reduced in the captured image, the foregoing method presents a problem that the total amount of noise is increased and an S/N ratio is reduced as compared with an image captured by a normal one-shot exposure, resulting in degradation in image quality of a dark region in particular.
Further, in order to prevent degradation in image quality of a dark region, the number of images acquired in a time-division manner may be reduced and a multi-shot exposure time may be increased. However, in that case, motion blur occurs in each of continuously captured images. Moreover, when motion blur has occurred, alignment accuracy in superimposing and adding a plurality of continuously captured images is also degraded. Accordingly, there arises a problem that sufficient camera shake correction cannot be performed.